Samudranil Pal

SYNTHESIS, STRUCTURE AND PROPERTIES OF A DICOPPER(II) COMPLEX

Abstract A dinuclear copper(II) complex, [Cu2(bhsNO2)2(H2O)2] was isolated by reacting Cu(O2CCH3)2·H2O and 2-hydroxy-5-nitrobenzaldehyde benzoylhydrazone (H2bhsNO2) in methanol. The X-ray structure of the complex has been determined. The dinegative ligands bind the Cu(II) ions through the deprotonated amide–O, imine–N and phenolate–O atoms. The pair of Cu(II) ions are linked by the two phenolate–O atoms. The coordination geometry around each Cu(II) is square pyramidal. The imine–N, amide–O and the bridging phenolate–O atoms form the square plane and the oxygen atom of a water molecule occupies the axial coordination site. The complex is redox active. Variable temperature (25–300 K) magnetic susceptibility measurements in the solid state are consistent with an antiferromagnetic interaction between the two metal centres. The coupling constant J is found to be −186(5) cm−1 by least-squares fitting of the magnetic susceptibility data using an expression derived from the isotropic spin Hamiltonian, H=−2JS1·S2 (S1=S2=1/2).

Dimeric and polymeric square-pyramidal copper(II) complexes containing equatorial–apical chloride or acetate bridges

Syntheses, crystal structures and physical properties of four new copper(II) complexes of deprotonated aroylhydrazones of 2-pyridine-carboxaldehyde are reported. Two of the complexes contain chloride as a coligand and the other two contain acetate as a coligand. In each complex, the planar tridentate monoanionic ligand binds the metal ion via the pyridine-N, the imine-N and the amide-O atoms. The fourth site is satisfied by the chloride or the acetate-O to form a square-plane. In the solid state, both complexes containing the acetate as the coligand exist as centrosymmetric dimeric species with the metal ion in a distorted square-pyramidal coordination sphere and the acetate group acting as a monoatomic equatorial–apical bridge. One of the complexes containing chloride is a similar centrosymmetric dichloro-bridged dinuclear species. However, the other one exists as a polymeric chain species via equatorial–apical chloride bridges. The electronic spectra of the complexes in methanol solutions display a ligand-field band in the visible region (687–713 nm). The complexes are redox active and, in each case, two reduction responses are observed in the potential range −0.06 to −0.29 and −0.60 to −0.70 V (vs. Ag/AgCl) in methanol solutions. Cryomagnetic studies revealed that no significant spin–spin interaction is operative between the metal ions in any of these four complexes.

Vanadium(V) Complexes of O,N,O-Donor Tridentate Ligands Containing the {VVO(OMe)}2+ Unit: Syntheses, Structures and Properties

Abstract Syntheses, characterisation and properties of two complexes containing the oxovanadium(V) methoxide unit have been described. Deprotonated benzoylhydrazones of 2–hydroxy–5–methoxy‐benzaldehyde (H2bhsOMe) and 2–hydroxy–5–chlorobenzaldehyde (H2bhsCl) were used as coligands. Crystal structures of both the complexes were determined. In solid state one of them is a dinuclear species [VO(bhsOMe)(OMe)]2 (1) whereas the other one is a mononuclear complex [VO(bhsCl)(OMe)(HOMe)](2). The dinegative ligands coordinate the metal ions via phenolate–O, imine–N and deprotonated amide–O atoms. In 1, the metal ions of two square pyramidal VO(bhsOMe)(OMe) units share the methoxide groups to form a dinuclear species. The oxygen of a methanol molecule completes the hexacoordination of the metal centre in 2. In each of the two distorted octahedral VO5N moieties of 1 the bridging methoxide oxygen and in that of 2 the methanol oxygen is trans to the corresponding oxo group. Both the complexes are redox active. The VO3+ to VO2+ reduction potentials (vs Ag/AgCl) of 1 and 2 are observed at −0.25 and −0.04 V, respectively. The band positions in the electronic spectra and the redox potentials reflect the influence of the substituents present on the ligands.

A one-dimensional assembly of a square-planar copper(II) complex with alternating short and long Cu⋯Cu distances. Metal ion spin-exchange viaπ-π interactions

A mixed-ligand copper(II) complex, [Cu(bhac)(Hdmpz)], with a tridentate Schiff base, acetylacetone benzoylhydrazone (H2bhac) and a monodentate heterocycle, 3,5-dimethylpyrazole (Hdmpz), has been synthesized and characterized by analytical, infrared and electronic absorption spectroscopy, and cyclic voltammetry. The molecular structure of the complex has been determined by X-ray crystallography. The metal ion is coordinated to the enolate-O, the imine-N and the deprotonated amide-O centres of the deprotonated Schiff base (bhac2−) and to the sp2 N atom of Hdmpz. The coordination geometry around the metal centre is square-planar. There is no displacement of the metal centre from the N2O2 square plane. The whole molecule is essentially planar, barring a small variation in the orientation of the Hdmpz plane with respect to the {Cu(bhac)} plane. In the solid state, two types of π-π interactions on two sides of [Cu(bhac)(Hdmpz)] molecule lead to a one-dimensional arrangement of the complex with sequential short [3.5952(8) A] and long ([5.5960(12) A] Cu⋯Cu distances. Solid state as well as frozen solution EPR spectral measurements reveal an antiferromagnetically coupled dicopper(II) system and indicate a magnetic exchange interaction mediated by π-π interactions. Magnetic susceptibility data in the temperature range of 10–300 K are consistent with this observation. The magnitude of the coupling constant J, obtained by least-squares fitting of the data using the Bleany–Bowers expression, is −6.0(1) cm−1.

Square-planar nickel(II) complexes with a tridentate Schiff base and monodentate heterocycles: self-assembly to dimeric and one-dimensional array via hydrogen bonding

Abstract Two nickel(II) complexes having the general formula [Ni(bhac)L] with tridentate ONO-donor acetylacetone benzoylhydrazone (H2bhac) and monodentate N-donor heterocycles (L=3,5-dimethylpyrazole (Hdmpz) and imidazole (Himdz)) are reported. The complexes were synthesized in ethanol media by reacting Ni(O2CCH3)2·4H2O, H2bhac and L in 1:1:1 mole ratio and characterized by analytical, magnetic and spectroscopic methods. X-ray crystal structures of both complexes have been determined. In each complex, the metal ion is in square-planar N2O2 coordination geometry. In the solid state, a one-dimensional assembly of the [Ni(bhac)(Himdz)] molecules is formed via intermolecular hydrogen bonds between the imidazole N–H groups and the uncoordinated N-atoms of the deprotonated amide functionalities. On the other hand, two [Ni(bhac)(Hdmpz)] molecules are involved in a pair of complementary hydrogen bonds between the pyrazole N–H groups and the coordinated O-atoms of the deprotonated amide functionalities forming a dinuclear species.

Manganese(IV) in discrete O3S3 coordination

Preparation des complexes de Mn(IV) avec les coordinats thiohydroxamiques. Proprietes physiques, comportement redox et stereochimie

Copper(II) complexes with aroylhydrazones

The coordination chemistry of copper(II) with tridentate aroylhydrazones is briefly discussed in this article. Two types of aroylhydrazones derived from aroylhydrazines and ortho-hydroxy aldehydes or 2-pyridine-carboxaldehyde have been used. The characterization of the complexes has been performed with the help of various physico-chemical techniques. Solid state structural patterns have been established by X-ray crystallography. In the solid state, structural varieties of these complexes are seen to range from monomeric, dimeric, polymeric and one-dimensional self-assembly via hydrogen bonds and π-π interactions. EPR spectroscopy and variable temperature magnetic susceptibility measurements have been used to reveal the nature of the coordination geometry and magnetic characteristics of these complexes.

Copper(II)-activated transformation of azomethine to imidate: synthetic and structural studies

Abstract The Schiff base 2-pyridine–carboxaldehyde 4-dimethylaminobenzoylhydrazone (HL, 1) was prepared by reacting 2-pyridine–carboxaldehyde and 4-dimethylaminobenzoylhydrazine in a 1:1 molar ratio in methanol. Reaction of HL (1) with Cu(O2CCH3)2·H2O (in a 1:1 molar ratio) in methanol afforded a dinuclear copper(II) complex, [Cu2(μ-O2CCH3)2L′2]·2H2O (2). The azomethine functionality (CHN) of 1 is converted to imidate (C(OMe)N) in the complexed ligand L′−. Molecular structures of both 1 and 2 were determined by X-ray crystallographic studies. The dinuclear molecule of 2 is centrosymmetric and contains two monoatomic bridging acetate groups. Each copper(II) centre is in a square-pyramidal N2O3 coordination sphere. The ligand, L′− coordinates the metal ion via the pyridine-N, the imidate-N, and the deprotonated amide-O atoms. One of the acetate oxygen atoms completes the N2O2 square-plane. The oxygen of the symmetry-related acetate fills the apical coordination site. Structural parameters are consistent with both copper ions being in a +2 oxidation state. The room temperature magnetic moment is 1.89 μB (per Cu). In powder phase the complex displays an axial EPR spectrum at 298 K. The complex is nonconducting in methanol solution. The electronic spectrum shows a ligand field absorption at 680 nm and charge transfer bands in the range 426–215 nm.

Mononuclear Pervanadyl (VO2+) Complexes with Tridentate Schiff Bases: Self-assemblingvia C-H…oxo and π-π Interactions

Pervanadyl (VO2+) complexes with N-(aroyl)-N′-(picolinylidene)hydrazines (HL = Hpabh, Hpath and Hpadh; H stands for the dissociable amide hydrogen) are described. The Schiff bases were obtained by condensation of 2-pyridine-carboxaldehyde with benzhydrazide (Hpabh), 4-methylbenzhydrazide (Hpath) and 4-dimethylaminobenzhydrazide (Hpadh), respectively. The reaction of [VO(acac)2] and HL in acetonitrile in air affords the complexes of general formula [VO2L]. The diamagnetic nature and EPR silence confirm the +5 oxidation state of vanadium in these complexes. Infrared spectra of the complexes are consistent with the enolate form of the coordinated ligands. Electronic spectra show charge transfer bands in the range 486–233 nm. The complexes are redox active and display an irreversible reduction (–0.64 to –0.72 V vs. Ag/AgCl). The crystal structures of all the complexes have been determined. In each complex, the metal centre is in a distorted trigonal-bipyramidal N2O3 coordination sphere formed by the pyridine-N, the imine-N and the deprotonated amide-O donor L– and two oxo groups. The planar ligand satisfies one equatorial and two axial positions. The other two equatorial positions are occupied by the two oxo groups. In the solid state, the molecules of each of the three complexes form a chain-like arrangement via the azomethine-H…oxo interactions. Interchain weak π-π interactions lead to two dimensional networks for [VO2(pabh)] and [VO2(path)]. On the other hand, [VO2(padh)] forms a two-dimensional network through interchain N-methyl-H…oxo interactions. Mononukleare Pervanadyl(VO2+)-Komplexe mit dreizahnigen Schiffschen Basen: Strukturaufbau via C–H…oxo- und π-π-Wechselwirkungen Pervanadyl(VO2+)-Komplexe mit N-(aroyl)- N′-(picolinyiden)hydrazinen (HL = Hpabh, Hpath und Hpadh; H steht fur abdissoziierbaren Amidwasserstoff) werden beschrieben. Die Schiffschen Basen wurden durch Kondensationsreaktionen von 2-Pyridincarboxylaldehyd mit Benzhydrazid (Hpabh), 4-Methylbenzhydrazid (Hpath) bzw. 4-Dimethylaminobenzhydrazid (Hpadh) erhalten. Die Reaktion von [VO(acac)2] und HL in Acetonitril an Luft ergibt die Komplexe der allgemeinen Formel [VO2L]. Die diamagnetische Natur und fehlende EPR-Signale bestatigen den Oxidationszustand +5 des Vanadiums in diesen Komplexen. Die IR-Spektren der Komplexe stehen in Ubereinstimmung mit der Enolat-Form der Liganden. Die Elektronenspektren zeigen Chargetransfer-Banden im Bereich von 486 bis 233 nm. Die Komplexe sind redox-aktiv und zeigen eine irreversible Reduktion (–0,64 bis –0,72 V vs. Ag/AgCl). Die Kristallstrukturen aller Verbindungen wurden bestimmt. In jedem Komplex liegt das Metallatom in einer verzerrt-trigonal-pyramidalen N2O3-Koordinationssphare vor, die aus dem Pyridin-N-Atom, dem Imin-N-Atom und dem deprotonierten Amid-O-Atom des Donors L– und zweier Oxogruppen gebildet wird. Die planaren Liganden besetzen eine aquatoriale und zwei axiale Positionen. Die anderen zwei aquatorialen Positionen werden durch die zwei Oxogruppen besetzt. Im festen Zustand bilden die Molekule der drei Komplexe eine kettenartige Anordnung uber die Azomethin-H…Oxo-Wechselwirkungen. Schwache π-π-Wechselwirkungen zwischen den Ketten fuhren zu einem zweidimensionalen Netz bei [VO2(pabh)] und [VO2(path)]. [VO2(padh)] bildet eine zweidimensionale Struktur durch N-Methyl-H…Oxo-Wechselwirkungen.

A one-dimensional assembly of copper(II) polyhedra via dual use of hydrogen-bonding and π–π interaction

Abstract A copper(II) complex [Cu(Hpadh)Cl2] with pyridine-N, imine-N and amide-O coordinating 2-pyridine-carboxaldehyde 4-dimethylaminobenzoylhydrazone (Hpadh) has been synthesized and structurally characterized. In the solid state, each square–pyramidal Cu(Hpadh)Cl2 unit is connected to one neighbour by a pair of hydrogen bonds between the amide-H and the apical chloride and to the other by a couple of π–π interactions between the aromatic rings of the coordinated ligands forming a novel chain-like arrangement of copper(II) centres with successive long and short Cu···Cu distances. Variable temperature (300–18 K) magnetic susceptibility measurements showed that the complex is essentially Curie paramagnetic.